Normal labor is generally divided into three stages: the first stage begins with the onset of labor and ends when dilatation of the cervix is complete; the second stage begins at that point and ends with the complete birth of the baby; and this is followed by the third stage which ends with the delivery of the placenta. During labor it is common to use either an external ultrasonic system for recording the baby's heart rate, and an external system for detecting the mother's uterine contractions, or an electronic system to sense the baby's heart pulses by an electrode attached to the baby's head and the mother's contractions by a pressure catheter applied to the mother inside the uterus.
However, a number of other physiological conditions of the mother and baby during labor can also be monitored in order to determine the progress of labor. These additional conditions include: (1) effacement (the thinning out of the cervix that occurs before and during the first stage of labor); (2) cervical dilatation (the increase in size of the cervical opening); (3) position of the cervix (the relation of the cervix to the vaginal axis, normally the fetal head); (4) station (the level of a predetermined point of the fetal presenting part with reference to the mother's pelvis), (5) position of the head which describes the relationship of the head to the pelvis and (6) and presentation which describes the part of the fetus (such as brow, face or breech) at the cervical opening.
The more common determination of station is the distance between the tip of the fetal head and the ischial spines which can be palpable by the physician; but a more accurate determination of station is the distance between the bi-parietal diameter (BPD) of the fetal head and the mother's pelvic inlet.
The foregoing conditions are generally determined by a physical examination, e.g., by the insertion of a finger through the mother's vagina. However, the accuracy of such a “finger” examination is very subjective and depends to a great extent on the experience, judgment, and even finger size, of the physician. Other drawbacks in such a physical examination are that it can be done only at spaced intervals, it generally produces discomfort to the mother, and it involves a number of risks including contamination, infection, dislodgment of a fetal monitor, injury to the baby, etc. Failure to interpret the precise stage of the labor progress from the physical examination can result in injury or even death of the baby or of the mother.
Many devices have been proposed in the past for automatically monitoring these conditions. As examples, U.S. Pat. No. 4,476,871 proposes an elongated tube having electrodes spaced along its length to monitor cervical dilatation during labor; U.S. Pat. Nos. 4,942,882 and 5,135,006 propose a fetal monitor probe attached to the fetal head to monitor heart beat, which probe is calibrated to monitor progress of descent; U.S. Pat. No. 5,222,485 proposes an elongated inflatable sac to monitor the position of the fetus and the configuration of the cervix; and U.S. Pat. No. 5,406,961 proposes a pessary to monitor the configuration of the cervix. However, for one reason or another, none of the previously proposed devices has come into any widespread use, and the historical “finger” examination continues to be the one in common use to this day.
Recent studies (Sherer et al., Ultrasound Obstet Gynecol 2002 March; 19(3)):258-68) have demonstrated a high rate of error (75% and 65%) in transvaginal digital determination of fetal head position during active labor and the second stage of labor (respectively). The inaccurate assessment of the station or the position of the head also lead to decisions to use forceps or vacuum when the baby's head is too high in the birth canal, as well as delay in performing C-section when needed. In both cases the end result can be lethal to the fetus and highly damaging to the mother.
Moreover, the “digital (finger) test” can cause infections, and is forbidden in cases of early amniotic rupture. It also puts a heavy workload on the delivery room staff, particularly during peak periods. Furthermore, since the digital examination is intermittent, trends and sharp changes in the progress of labor are sometimes missed, again leading to potentially wrong decisions. Also, multiple digital examinations increase the risk of inflammation.
U.S. Pat. No. 6,200,279 to Paltieli, incorporated herein by reference in its entirety, describes improved methods and apparatus for monitoring the progress of labor. In one embodiment, the progress of labor is monitored by attaching a position sensor to a predetermined point on the mother's pelvic bones, monitoring the location of the position sensor in three-dimensional space relative to a reference, and monitoring the location of the fetal presenting part with respect to the predetermined point on the mother's pelvic bones. The location of the fetal presenting part may be indicated by a similar position sensor, or by imaging. Other conditions, such as effacement, cervical dilatation, and cervical position may also be monitored in a similar manner.
In U.S. Pat. No. 6,669,653, a continuation-in-part of U.S. Pat. No. 6,200,279, further embodiments are described. According to one aspect of U.S. Pat. No. 6,669,653, there is provided a method of monitoring the progress of labor in a mother during childbirth, comprising: attaching a position sensor to a predetermined point on the mother's pelvic bones; monitoring the location of the position sensor in three-dimensional space relative to a reference; monitoring the location of the fetal presenting part with respect to the predetermined point on the mother's pelvic bones to provide an indication of the progress of labor; and measuring the cervical dilation by attaching sensors to the cervix.
In another embodiment of U.S. Pat. No. 6,669,653, there is provided a method of non-continuous monitoring of the progress of labor in a mother during childbirth, comprising: using a probe or finger-mounted sensor to measure the fetal presenting part relative to a predetermined point on the mother's pelvic bone, and to measure the cervical dilation by touching the cervix in, for example, two points.
In another embodiment, the locations of the fetal presenting part and of the opposite sides of the end of the mother's uterine cervix may be monitored by position sensors attached to these respective elements. In a second described embodiment, the latter are monitored non-continuously using a hand held probe or finger-mounted sensor. In a third described embodiment, the latter are monitored by operating an ultrasonic transducer to image the mother's cervix and pelvic bones, and the fetal head, on a screen, and by using a position sensor on the ultrasonic transducer, and a marker for marking the screen, to locate the positions of these elements. A fourth embodiment is described utilizing at least two sensors, one of which is attached to a bony position on the pelvis to serve as the reference point, and the others may first be used to map the pelvis from outside of the body and to map the BPD plane by attaching it to the ultrasound probe, to map the ischial spines and ischial tuberosities from the inside and then to be attached to the cervix and fetal presenting part.
In a further embodiment of U.S. Pat. No. 6,669,653, position sensors may also be attached to, or position coordinates may be obtained of, the anterior superior iliac spine, the pubic symphysis, the scrum at 1-3 levels, the ischial spines and the ischial tuberosity, and such positions may be used for mapping the pelvic inlet outlet and midpelvis. Such mapping or pelvimetry may be helpful in determining whether the head of the baby is of suitable size for passage through the birth canal.
According to further features in U.S. Pat. No. 6,669,653, the cervical dilatation of the mother's cervix is continuously indicated by monitoring the positions of the position sensors applied to the opposite sides of the end of the cervix, and continuously displaying the spatial distance between them. The position of the fetal presenting part (e.g., fetal head) is also continuously indicated by monitoring and displaying their respective locations.
In another embodiment, the cervical dilatation of the mother's cervix and the position of the fetal presenting part or the BPD are monitored on a non-continuous basis by touching a probe or finger-mounted sensor to each side of the cervix and a pre-determined point or points on or connected to the fetal head.
According to further features in U.S. Pat. No. 6,669,653, the above conditions are computed and displayed in the form of units of distance (e.g., cm), and/or in the form of a graph, which may be called a partogram, showing the interrelation of the cervical dilatation and the descent of the fetal presenting part. Furthermore, such display may include an image of the fetus within the birth canal and the relation and orientation over time of the head to the pelvic inlet, outlet and midpelvis. FIG. 4A presents an illustration of a display of position of the presenting part in various stages of labor, in accordance with an embodiment of U.S. Pat. No. 6,669,653. Other methods to display such information may be used.
According to a further embodiment of U.S. Pat. No. 6,669,653, there is provided an apparatus for monitoring the progress of labor in a mother during childbirth, including: at least two sensors, one of which is attached to a bony position on the pelvis 8 to serve as the reference point, and another may first be used to map the pelvis from outside of the body, to map the BPD plane by attaching it to the ultrasound probe, to map the ischial spines and ischial tuberosities from the inside and then to be attached to the fetal presenting part, and may be attached to the sides of the cervix.
The output device is preferably a display, but could be a plotter, recorder, or other device for displaying, recording, and/or processing the data outputted by the computer
Such a method and apparatus permits the progress of labor to be monitored in a manner which is either continuous or intermittent, which is less dependent for accuracy on the experience, judgment or finger size of the attendant in the conventional “finger examination”, which subjects the mother to less discomfort, and which involves less risk of contamination, infection, dislodgment of a fetal monitor, or injury to or death of the baby or mother due to a wrong assessment of the fetal position or of labor progress. Moreover, this technique enables more precise monitoring of the critical condition, namely the changes in the spatial distance of the BPD of the baby's head with respect to the pelvic inlet.